Traditional light oil reserves are being depleted due to high oil production. Oil fields are requiring substantial new investment in secondary and tertiary oil recovery technology. On the other hand, the cost of producing and refining heavy crude has decreased due to new production and refining technologies. Most of the heavy crude reserves all over the world have not yet been exploited. Considering the continuously increasing demand in oil and the large difference in price between light oil and heavy crude, heavy crude reserves are emerging as a very attractive source of energy.
Heavy crude contains 40-70% high boiling range material that boils over 1000° F. (i.e., vacuum resid) and very low amounts of fuels in high demand such as, for example, gasoline and diesel. Therefore, in order to convert vacuum resid to valuable light products, new and more cost effective technologies are needed. Heavy crude can be converted into lighter products via conventional processes such as coking (e.g., delayed coking and/or fluid coking) and hydroconversion (e.g., LC Fining and H-OIL). However, such conventional processes produce large amounts of undesirable byproducts such as, for example, coke or fuel oil and also are very sensitive to the contaminants such as, for example, V, Ni, and S.
Most hydroconversion technologies utilize novel catalysts composed predominantly of metals of Group VA, VIA, VIIA, or VIII metal sulfides especially compounds such as molybdenum disulfide (MoS2) and nickel sulfide (NiS). Such metals are highly active in hydroconversion of heavy crudes but also are very expensive. In order to minimize the amount of catalyst required, and minimize the diffusion effects, catalyst is often unsupported.
In hydroconversion of vacuum resid and related feedstocks, the remaining portion of unconverted material, which may range from 0 to 10% of fresh feed, shows low API gravity (−10 to 29), high remaining microcarbon residue (MCR) (0 to 60%), very high viscosity and asphaltenes content, and likely also contains catalyst. Therefore, the separation scheme utilized to recover valuable active metals such as, for example, MoS2 and NiS is a critical step in making the process economically attractive. Catalyst remaining in the unconverted slurry bleed oil (USBO) is to be removed and sent for reprocessing to recover the metals and also to recover the unconverted portion of the residue in order to be recycled or further processed.
Expensive spent catalyst contained in the USBO is coated with USBO and is not leachable by conventional technologies of metals extraction that basically are effective for water-based slurries. Therefore, without additional processing, the valuable metals cannot be recovered. Technologies employing microfiltration, ultrafiltration, or nanofiltration; gravity based separation, such as centrifugation or hydrocycloning; and chemical recovery, which may be effective for water-based slurries, similarly do not provide acceptable results for catalyst coated with USBO.